The present invention relates to a process for the production of a catalytic converter for the cleaning of the exhaust gases produced by internal-combustion engines and, in particular, to a catalytic converter body through which the exhaust gases flow for catalytic conversion to less noxious gases. The present invention also relates to a catalytic converter body having improved structural characteristics.
Catalytic converters are being increasingly used in automotive engine technology to convert noxious exhaust gas components into harmless gases, with the intention being particularly directed to the reduction of the emission of carbon monoxide, hydrocarbons and nitrogen oxides from the engine. The principal components of such a catalytic converter assembly or cleaning unit are the catalytic converter carrier or converter body, its precious-metal catalytic coating, and a housing surrounding the catalytic converter body.
A honeycomb-like-structured ceramic cylinder with a circular or oval cross-section is generally used as a carrier for the catalytic converter. This type of unit has, until now, been the one which has met with the greatest success as compared to other carrier structures, such as, for example, porous beds of catalytic particles, and wound sheet-metal strips. The honeycomb character is created by a plurality of fine channels which run through the catalytic converter body in the direction of flow of the exhaust gases. The actual catalytic ingredient is normally coated on the surface of the catalytic converter body. Platinum, rhodium and palladium are primarily used as the catalytic constituent of the surface coating.
One problem which is difficult to overcome, in particular with the use of a catalytic converter body of ceramic, is its fracture-resistant mounting. This is due to the brittle nature of ceramic material. In this connection, the thin-walled honeycomb pattern of the catalytic converter body is extremely sensitive to vibrations, impact and other mechanical influences. Also to be taken into account are the exhaust gas flow impulses and the high exhaust gas temperatures, which may reach up to about 900.degree. C.
To avoid the risk of fracture due to external influences or normal motions of the ceramic body, the body is held in a highly heat-resistant wire shrouding. The use of bypass seals insures that the exhaust gases will not leak around the ceramic block and through the wire network. The ceramic body and the wire shroud network are, in general, surrounded by a catalytic converter housing which has the additional task of protecting the sensitive ceramic body from rapid changes in temperature, e.g , due to external splashing of water, and mechanical impacts.
Due to the costly production method and the necessary secure packaging of the catalytic converter body, such a catalytic converter is relatively expensive.
Accordingly, it is an object of the present invention to provide a catalytic converter body which has improved physical strength.
It is a particular object of the present invention to provide a catalytic converter body having improved fracture resistance.
It is another object of the present invention to provide a catalytic converter body which can be fabricated by less costly techniques.
It is a further object of the present invention to provide a catalytic converter body which possesses a good, or even more improved, catalytic effect with a simple structure.
These and other objects of the invention, as well as advantages thereof, will become more clear from the disclosure which follows.